Floral Ontogeny of Cercis (Leguminosae: Caesalpinioideae: Cercideae): Does It Show Convergence with Papilionoids?

Abstract

To determine whether convergence has occurred between Cercis and papilionoid flowers, floral ontogeny of Cercis canadensis and Cercis siliquastrum was studied using scanning electron microscopy and light microscopy. In racemes, the helically arranged, acropetally initiated bracts subtend individual flowers. Paired bracteoles are initiated successively by the floral apex. Sepals are helically initiated, beginning with a single sepal in a nonmedian abaxial position. The petals initiate unidirectionally from the abaxial side, and there is overlap in time between the last sepal and the first petal. The two stamen whorls initiate unidirectionally, starting from the abaxial side. Unusual features of organ enlargement include the two abaxial petals persistently larger during development than the other three and a late‐forming hypanthium that elevates the 10 stamens attached to its rim. During receptacle expansion the two stamen whorls merge into one. Adaxially, the filament bases arch around two fenestrations, o...